Activation and Dose Codes
Activation codes compute the radioactive inventory that neutrons induce in materials, and dose codes turn that inventory into radiation fields for shielding and safety.
Neutrons make materials radioactive
Fusion neutrons transmute the nuclei of structural and blanket materials, producing radioactive isotopes. Activation codes take the neutron flux spectrum from a neutron transport calculation and solve the coupled nuclear rate equations, the Bateman equations, to predict the isotopic inventory, its decay heat, and its residual radioactivity as functions of time after shutdown.
This is essential for waste classification, hands-on-maintenance planning, and safety analysis, since the induced activity, not the fusion reaction itself, dominates the radiological hazard after operation.
The Bateman solve
Given a neutron spectrum and reaction cross-sections, the code builds a network of production and decay pathways among thousands of nuclides and integrates the rate equations through irradiation and cooling. The output is the time-dependent activity, decay heat, and gamma source of each material region.
From inventory to dose
The gamma source from activated material drives a subsequent shielding transport calculation to compute the dose rate at maintenance locations. This shutdown-dose-rate analysis determines whether components can be approached by workers or require remote handling, closing the loop from neutronics to occupational safety.
Design relevance
For the deuterium-tritium Hyperion breeder, whose 14 MeV neutrons drive the tritium-breeding blanket toward a breeding ratio of 1.8, activation and dose analysis guides material selection toward low-activation choices and sizes the shielding. These are simulation studies informing design ahead of construction.
- Solves Bateman equations for induced inventory
- Predicts decay heat and residual activity
- Feeds shutdown-dose-rate shielding analysis
- Guides low-activation material choices